When a person contracts HIV, his or her immune system starts to produce antibodies against the virus to ward off infection. Although these antibodies are not effective in fighting HIV, it is their presence in the blood that results in a positive HIV test. This test can be conducted at an STD clinic, a government funded HIV testing site, a hospital, or a doctor's office. The screen can be done in a number of ways, but the most common is a conventional blood test. In this case, a sample is drawn by a health care provider and sent to a lab for screening. A similar HIV test involves an oral fluid sample which is swabbed from the inside of the mouth before being tested. A slightly less accurate method involves a urine sample.